There is an ongoing concern in the tobacco industry to produce cigarettes having wrappers which reduce the ignition proclivity of the smoking article, or the tendency of the smoking article to ignite surfaces which come into contact with the lit smoking article. Reports have been made of fires attributed to burning cigarettes coming into contact with combustible materials. A justifiable interest exists in the industry to reduce the tendency of cigarettes, or other smoking articles to ignite surfaces and materials used in furniture, bedding, and the like upon contact.
Thus, a desirable feature of smoking articles, particularly cigarettes, is that they self-extinguish upon being dropped or left in a free burning state on combustible materials.
It has long been recognized in the tobacco industry that the cigarette wrapper has a significant influence on the smolder characteristics of the cigarette. In this regard, various attempts have been made in the art to alter or modify the cigarette wrappers in order to achieve the desired tendency of the cigarette to self-extinguish, or in other words to reduce the ignition proclivity characteristics of cigarettes.
The prior art describes the application of film-forming solutions to cigarette paper to reduce the paper permeability and control the burn rate. It has been shown that when these materials have been applied in discrete areas along the length of the cigarette, the cigarette shows a reduced propensity to ignite a substrate, tends to self-extinguish, and has a higher puff count.
U.S. Pat. No. 5,878,753 to Peterson which is incorporated herein by reference, for example, describes a smoking article wrapper being treated with a film-forming aqueous solution to reduce permeability. U.S. Pat. No. 5,878,754 to Peterson which is also incorporated herein by reference describes a smoking article wrapper being treated with a non-aqueous solution of a solvent soluble polymer dissolved in a non-aqueous solution to reduce permeability.
In some cases, when a solution is applied to the paper wrapper and dried there is a tendency for the paper to experience non-uniform dimensional changes. In particular, applying coatings in the form of bands can cause the bands to shrink relative to the uncoated paper, causing the uncoated areas to bulge out.
Although some improvements have been made in the art, there is still a need for an improved method for producing a cigarette wrapper with reduced ignition proclivity properties. Specifically, a need exists for an improved method of applying a film-forming solution to a paper wrapper in discrete areas for decreasing the permeability of the wrapper without causing non-uniform dimensional changes in the wrapper or otherwise adversely affecting the appearance of the wrapper.
The present invention is generally directed to paper wrappers for smoking articles with reduced ignition proclivity and to a process for making the wrappers. For example, in one embodiment, the process includes the steps of providing a paper wrapper made from a paper web. For example, the paper wrapper can contain flax fibers, softwood fibers, hardwood fibers and mixtures thereof. The paper wrapper can also include a filler, such as calcium carbonate, in an amount from about 10% to about 40% by weight.
In accordance with the present invention, multiple layers of a film-forming composition are applied to the paper wrapper at particular locations. The multiple layers of the film-forming composition form treated discrete areas on the wrapper. The discrete areas are separated by untreated areas. The treated discrete areas have a permeability within a predetermined range sufficient to reduce ignition proclivity. For example, the treated areas can reduce ignition proclivity by reducing oxygen to a smoldering coal of the smoking article as the coal burns and advances into the treated areas.
In one embodiment of the present invention, the paper wrapper is dried in between application of each layer of the film-forming composition. The paper wrapper can be dried by being contacted with a hot gas stream, by being placed in contact with a steam can, by being with infra-red rays or can simply be air dried.
The film-forming composition can be can be applied to the paper wrapper according to various methods. For example, the multiple layers can be printed onto the paper using, for instance, flexography, direct gravure printing, and offset gravure printing.
In one embodiment, the discrete areas formed by the film-forming composition are in the shape of circumferential bands disposed longitudinally along the smoking article. The bands can have a width of greater than about 4 mm, such as from about 5 mm to about 10 mm. The bands can be spaced from each other at a distance of from about 5 mm to about 30 mm and particularly from about 5 mm to about 20 mm.
The film-forming composition can be made from any suitable material that will provide the desired burn characteristics. Examples of film-forming composition that can be used include alginate solutions, pectin solutions, silicate solutions, starch solutions, carboxymethyl cellulose solutions, other cellulose derivative solutions, guar gum solutions, and mixtures thereof. If desired, the film-forming composition can include a filler, such as chalk, clay, a metal oxide, calcium carbonate, or mixtures thereof.
The amount of the film-forming composition that is applied to the paper wrapper depends upon the particular application and various factors. The amount applied to form each layer of the treated discrete areas can also vary depending upon the particular application. For example, in one embodiment, the film-forming composition can be applied to form a relatively light layer initially. Subsequently, heavier layers of the composition can be formed.
Alternatively, the film-forming composition can initially be applied as a relatively heavy layer. Lighter layers can then be placed on the heavier layer subsequently.
In still another embodiment of the present invention, a paper wrapper having reduced ignition proclivity characteristics is formed from a paper web having a relatively high permeability. For instance, the paper web can have a permeability of greater than about 60 Coresta, such as from about 60 to about 110 Coresta, and more particularly from about 60 to about 90 Coresta. A film-forming composition can then be applied to the paper web to form treated discrete areas with reduced ignition proclivity. The treated discrete areas can be formed from multiple layers of the film-forming composition.
Besides being directed to a process for reducing the permeability of a paper, the present invention is also directed to the paper wrapper itself and to smoking articles made from the paper wrapper. For example, a smoking article can include a tobacco column surrounded by a wrapper. The wrapper can be made from a paper web as described above.
In accordance with the present invention, the paper wrapper can include treated discrete areas separated by untreated areas. The treated discrete areas can be made from a multi-layered film and can have a permeability within a predetermined range sufficient to reduce the ignition proclivity properties of the article. For example, the treated areas can have a permeability of less than about 25 Coresta units, particularly less than 15 Coresta units, and more particularly from about 2 Coresta units to about 10 Coresta units.
The multi-layered film applied to the paper wrapper can be made according to the process described above. The amount of layers used to make the film can vary depending upon the particular application. For most applications, the film will contain at least two layers, and particularly from about three to about eight layers.
Other features and aspects of the present invention are discussed in greater detail below.